LEDs have the potential to revolutionize the efficiency, appearance, and quality of lighting. According to the United States Department of Energy, about 49 million LEDs were installed in the United States in 2012, saving about $675 million in annual energy costs. Switching entirely to LED lights over the next two decades could save the U.S. $250 billion in energy costs, reduce electricity consumption for lighting by nearly 50 percent, and avoid 1,800 million metric tons of carbon emissions. See http://energy.gov/articles/top-8-things-you-didn-t-know-about-leds.
Switching over to LED lighting, however, is not without challenges. LED lighting requires DC current to flow through the LEDs and, as such, the LEDs cannot simply be dropped in as replacements for incandescent lights, which use AC voltage. For the same reason, LEDs cannot be connected directly to dimmers that were designed for incandescent lights, as such dimmers control lighting by adjusting the RMS (root mean square) value of the AC voltage supplied to the incandescent lights. These dimmers use a technique called “phase cut” that suppresses a portion of the AC voltage to reduce the RMS value of the AC voltage.
There are generally two types of phase cut dimmers: forward phase cut (leading edge) dimmers, and reverse phase cut (trailing edge) dimmers. In a forward phase cut dimmer, the AC voltage from the line AC is cut or chopped at the front end of each half wave. In a reverse cut dimmer, the AC voltage from the line AC is cut or chopped at the back end of each half wave. In either case, the remaining uncut phase of the AC voltage results in a reduced RMS value. And because the phase cuts are typically made in predefined time intervals or increments that are usually too small for the human eye to discern, the dimming appears smooth and flicker-free.
But as both forward phase cut and reverse phase cut dimmer types are still AC voltage devices, neither dimmer type is suitable for LED lighting without significant modifications. Most LEDs and other SSL applications therefore have a fixture that includes a driver for driving the SSL. The SSL driver typically includes a power converter such as a switch mode power supply that converts AC line voltage to DC current to drive the SSL. The power converter typically has an AC/DC constant voltage converter that takes the AC line voltage and outputs a relatively constant DC voltage. A DC/DC constant current converter then converts the DC voltage to a relatively constant DC current to drive the SSL. Such an arrangement conceptually allows SSL fixtures to be used with phase cut dimmers available for incandescent lights.
In practice, however, a problem may sometimes arise with flicker and other visual anomalies when using existing phase cut dimmers with SSL fixtures. Flicker and other visual anomalies can be seen when there are sufficiently large ripples in the DC current provided to the SSL. The ripples result from an incompatible interaction between the phase cut dimmer and the switch mode power supplies and/or other elements of the SSL fixture. The problem often arises when a phase cut dimmer from one manufacturer is being used with an SSL fixture from a different manufacturer. This lack of compatibility has required dimmer manufacturers to list on their product literature and packaging which dimmers are compatible with which SSL fixtures, and vice versa.
Moreover, existing dimmers are largely non-interactive, consisting mainly of wall-mounted sliding switches, knobs, pads, and dials that have to be manually adjusted by a user each time the user wants to adjust room lighting. And while some programmable dimmers exist that can adjust lighting automatically in response to ambient light sensors and other inputs, these dimmers have heretofore been wired systems that require the sensors and other inputs to be transmitted over cables or wiring. In order to use a wireless sensor with such dimmers, a centralized coordinator device typically is needed to receive the signals from the wireless sensor and transmit them to the dimmer, which adds costs and complexity.
Thus, a need exists for an improved way to provide dimming for SSL fixtures, and particularly for a dimmer that is interactive, wireless, and capable of avoiding flicker and other visual anomalies for different types of SSL fixtures from various manufacturers.